A leading Syrian opposition group has picked a secular Kurd as its new leader, after criticism that the former head was too autocratic and the group was becoming dominated by Islamists.

The opposition is trying to pull together and appear more inclusive – its disarray has frustrated attempts to dislodge the Syrian president, Bashar al-Assad.

On Sunday, government forces shelled rebel-held cities and villages, killing at least 38 people in the Homs area, activists said. It was impossible to independently confirm the death toll.

The choice of Abdulbaset Sieda as head of the Syrian National Council – which has only tenuous ties to the Free Syrian Army, which is doing most of the fighting against Assad's forces – is aimed at achieving several goals.

Firstly, to counter criticism that the group is dominated by Islamists, especially the Muslim Brotherhood. Secondly, it is seen as an attempt to get Syria's minority Kurds to take a more active role in the uprising. Up to now they have stayed mostly on the sidelines.

Thirdly, the move could help counter criticism that under outgoing leader Burhan Ghalioun the umbrella organisation was too autocratic.

"This is clearly an opportunity and there is clearly a need for a change," said Peter Harling of the Brussels-based thinktank Crisis Group.

Sieda, 56, an expert on ancient civilisations, is an exile who lives in Sweden. His predecessor is based in Paris. Activists fighting in Syria worry that if they succeed in deposing Assad, the exiles will return and take over.

The SNC must also gain the confidence of the international community, which is searching for effective ways to hasten the departure of Assad.

William Hague, the foreign secretary, said on Sunday that he could not rule out military intervention in Syria, saying the situation is beginning to resemble the violence that gripped Bosnia in the 1990s.

Hague told Sky News that time was "clearly running short" to implement international envoy Kofi Annan's ceasefire plan. It was supposed to take effect on 12 April but never took hold.

Hague said Syria was "on the edge of collapse or of a sectarian civil war so I don't think we can rule anything out".

Sieda said his priority would be to expand and restructure the council to include more opposition figures, particularly from Syria's religious minorities.

"We are now in the process of repairing the relationship between the SNC and the forces working inside Syria so that we may reach common ground among us," Sieda said.

As the opposition was reorganising, the death toll mounted with Syrian troops fighting to regain control of rebel-held areas scattered through the country.

Seventeen people were killed in the city of Homs and surrounding towns, said Rami Abdul-Rahman of the Syrian Observatory of Human Rights. He said at least 16 Syrian forces were also killed in clashes throughout the country.

In the aftermath of the clash in Homs, amateur video showed chaos in an underground medical treatment site where the wounded lay. The footage reportedly showed one man with horrific leg injuries, a dead boy and another man close to death.

The town of Qusair was a main target on Sunday, where at least six people were killed.

"The mortars came down on Qusair by the dozens," said Abu al-Hoda, a Qusair-based activist. He said women and children have been huddled for days in basements of apartment buildings, too fearful to come out.

Regime forces also shelled the southern city of Dera'a and nearby villages, said Abdul-Rahman.

The military unleashed heavy shelling and sent reinforcements to a mountainous area near the coastal city of Latakia, where hundreds of rebels have set up a base and fierce fighting has raged in recent days.

Fighting between government troops backed by helicopter gunships and armed groups in the area of Haffa broke out on Tuesday. Abdul-Rahman said at least 58 soldiers have been killed and more than 200 wounded since the operation began.